Mysterious high pitched sound...

[allman]

Hi,

Today my 1993 Astro 2WD CL EXT started making a constant, loud, high pitched sound. It goes away when I push the gas pedal (a little weight on it is enough) but it starts again if I lift my foot a little (letting the pedal come back up). Definitively coming from the engine somewhere, becomes louder if I open the hood. It goes like this: beeeeeeeeeeeeeeep. Disappears about half a second after ignition is turned off.

It isn't the radio (it's off).
It isn't the heater / ventilator / AC (it's off).
I checked the serpentine belt, it seems / feels OK (not loose).

It's really annoying, gave me a headache after 5 minutes.

What can it be?

Allman

[paintdrying]

Pinion bearing?

[sasktrini]

vacuum leak?

[94 Van Guy]

x2 on the vacuum leak. Had a check valve do the same thing.

[RECox286]

Yeah, I think I'll cast my vote for "B.F. Vacuum Leak".

Bob

[allman]

Hi,

Thanks for the tips.

Update:
1. Sound does not go away if I push the gas when shifter is in Neutral (when there is no real load on the engine).

2. Sound was 100% absent in the morning (chilly/damp morning) but became gradually noticeable after 10 minutes of driving (it faded in slowly). However, it didn't get so loud as yesterday afternoon (weather was considerably warmer yesterday and I didn't drive far today).

3. Rough idle / engine stumbling when accelerating or driving uphill has been coming and going for months before the sound appeared (checked fuel filter, ignition, O2 sensor, etc. many times but it still doesn't run well - until now I thought that problem was electrical; but maybe it's related to the vacuum leak?).

If it's a a vacuum leak: can I fix it myself? Which tubes/things to check? Should I have it serviced right away?

Allman

[chevymaher]

Hi,

Thanks for the tips.

Update:
1. Sound does not go away if I push the gas when shifter is in Neutral (when there is no real load on the engine).

2. Sound was 100% absent in the morning (chilly/damp morning) but became gradually noticeable after 10 minutes of driving (it faded in slowly). However, it didn't get so loud as yesterday afternoon (weather was considerably warmer yesterday and I didn't drive far today).

3. Rough idle / engine stumbling when accelerating or driving uphill has been coming and going for months before the sound appeared (checked fuel filter, ignition, O2 sensor, etc. many times but it still doesn't run well - until now I thought that problem was electrical; but maybe it's related to the vacuum leak?).

If it's a a vacuum leak: can I fix it myself? Which tubes/things to check? Should I have it serviced right away?

Allman

Yes you van fix it yourself.This one of the simpler things.Just follow the noise it telling on itself.And whatever leaking will look terrible when you get to it.Rotted hoses etc.

[RECox286]

Possibly an intake leak, but my gut says look in the vicinity of the accumulator plumbing.

Bob

[cowboydan]

video would help

[allman]

Hi,

Thanks again for tips. I'll try to make a video / sound recording in a few days (quite busy now).

Which hoses should I inspect? (tons of them...)

Allman

[allman]

Hi again,

I made some videos today: http://tinyurl.com/astronoise - PLEASE have a look. What could it be?

Video #1: driving to a nearby parking lot.
Video #2: driving back.

Notice that the "scream" disappears when I get up to decent speed on the road (gas pedal half way down, RPM goes up) and re-appears as soon as I start lifting my foot off the pedal. It's driving me crazy...

I didn't see any damaged/bad hoses (not sure where to look).

Allman

[94 Van Guy]

Have you looked at the intake? (maybe a tree leaf is in there) check the big vacuum hoses, maybe the positive crankcase ventilation system.

Good luck,

Keith

[cowboydan]

that noise is loud enough to pinpoint. divide the engine into 4 sections. 2 sections up front and 2 sections in the cab. once you pinpoint which quadrant the noise is, you then will only have a limited amout of lines. you can take video of all four sections but i think you will locate the source before. be mindfull of the fan and the coil when searching. removal of the air filter may create a bit more room for your flashlight. once you find the quadrant, if you still can't find the source, shoot some close up video of the quadrant. good effort on the video, it's just not much help from a stationary camera position

[chevymaher]

There a couple vacuums that are plastic tubes.To make a noise that loud I woud think one cracked and it vibrating like crazy like a whistle.Just start running your hands over stuff while it runnig.As bad as it leaking pitch of sound will change if you touch it.

[cowboydan]

i wonder if there is a code? there has got to be other symptoms than just a noise you would think anyway.

[allman]

Hi,

Thanks again for your replies. I'm getting the following error codes:

- 35 idle air control sensor circuit fault
- 44 oxygen sensor lean exhaust

Where is the "idle air control sensor circuit"?
The O2 sensor code has been coming and going after I changed the O2 sensor so I guess it's not related to the "scream", but any tips on that would be appreciated as well.

I can't see any plastic tubes that go into the engine block, isn't all air supposed to go through the air-filter assembly which sits on top? I might have misunderstood something. If possible: please provide more detailed instructions (step one: do this, step two: do that, etc.) 'cause I'm not sure where the "accumulator plumbing", "positive crankcase ventilation system", etc. is. How thick are those vacuum tubes and where exactly do they go? Top-left? Top-right? I can see other tubes but they are converted to metal before they reach the engine block and I bet they contain coolant not air.

Allman

[94 Van Guy]

The positive crankcase ventilation system, PCV, connects to the top of the valve cover on the passenger side of the engine. The tubing is about the size of your index finger. There is a metal part, the valve, that sits into a rubber grommet in the middle of the valve cover. I can't find a photo, but if I do I will let you know where tot look.

Hope that helps,

Keith
Found this, it may help

[chevymaher]

Actually if you got a serious vacuum leak it would cause it to be lean.Cylinders affected getting more air than gas.than other cylinders not as affected.some cylinders near the leak getting more air but same amount of gas if that makes sense.

[DMT00]

I have the exact same symptoms. Loud "beeeeeeeeeeep" at idle. No codes. No drive-ability issues. I would really like to get this fixed. Have you resolved this yet?

2000 LT AWD 143,xxx miles.

[DMT00]

After removing the dog house again I noticed the sound is coming from the fuel injector area. Move it or cover it with your hand and the sound changes. I was told you have to remove the intake manifold to replace it. Is this true? Spraying brake clean all around the area does not result in a raise of the idle. Is there a chance the injector is bad or damaged causing this noise?